Interspecific Introgressive Origin of Genomic Diversity in the House Mouse

We report on a genome-wide scan for introgression in the house mouse (Mus musculus domesticus) involving the Algerian mouse (Mus spretus), using 20 samples from the ranges of sympatry and allopatry. Our analysis reveals significant variability in introgression signatures along the genomes, as well as across the samples. We find that fewer than half of the chromosomes in each genome harbor all detectable introgression. Further, a surprising result is that European mice carry more M. spretus alleles than the sympatric African ones. Using the length distribution and sharing patterns of introgressed genomic tracts across the samples, we propose three hypotheses. First, at least three distinct hybridization events involving M. spretus have occurred, one of which is ancient, and the other two are recent. Second, several of the inferred introgressed tracts contain genes that are likely to confer adaptive advantage. Third, introgressed tracts might contain driver genes that determine the evolutionary fate of those tracts. Further, our analysis revealed introgressed genes of functional importance, including the Vkorc1 gene, which is implicated in rodenticide resistance, and olfactory receptor genes. Our findings highlight the extent and role of introgression in nature, and call for careful analysis and interpretation of house mouse data in evolutionary and genetic studies. Six wild M. m. domesticus samples were genotyped using the Affymetrix Mouse Diversity Genotyping Array.